To provide a better understanding of normal myocardial perfusion and to establish a data base against which to compare the results of studies in patient populations, we evaluated 51 healthy volunteers using exercise Thallium-201 emission-computed tomography. Cardiac disease was excluded to these volunteers on the basis of a normal history, physical examination, echocardiogram, chest radiograph and resting and exercise electrocardiograms. All subjects were able to exercise to the point of limiting fatigue or shortness of breath. At peak exercise, Thallium-201 was injected by peripheral vein and exercise was continued for an additional minute to allow for adequate circulation of the isotope. Rotational tomographic imaging was begun within 10 minutes of exercise and again after a three hour delay. Anatomically comparable tomographic slices from each of the three major planes of the heart were then analyzed for the distribution and intensity of the isotope. A quantitative analysis program was developed based on a radial distribution method. Tomographic slices were divided into 32 sectors, each of which spanned 11.25 degrees. Determinations of both maximal and total sector activity were made and the results normalized to the maximal value for the entire heart. Wash out profiles were then constructed representing the change in activity between the initial and delayed studies. These programs have allowed us to easily construct normal data bases for both sexes. Patients with heart disease can be compared quickly with the values derived from the normal volunteers and the results of any Thallium perfusion study can be expressed objectively and quantitatively without the risk of observer bias. These methods will serve to automate and validate future interpretations for any patient population.